The present invention relates to copying machines and, more particularly, to a method and arrangement for preventing sheets from charring in such copying machines.
Electro-photographic reproducing machines or copiers of the type wherein an image is formed on an image-carrying sheet and is thereafter fixed by subjecting the sheet at a fixing station to the influence of heat are generally known in the art. Since the toner powder and/or the sheet have different optical and thermal characteristics, short bursts of heat energy are used to melt substantially only the toner powder on the sheet without causing the sheet itself to receive any significant amounts of heat which would otherwise damage the sheet. Reflective arrangements are also known which intensify the heat and thereby achieve some savings in input energy.
However, the prior art copiers have not proven altogether satisfactory in preventing the image-carrying sheets from being burned or charred in the event that the sheets take too long to be advanced through the work station where the toner powder is being fixed to the sheet. In particular, on account of the high heat energy density which is further intensified and directed by the reflective arrangement towards a sheet, the sheet tends to char in the event of partial or complete copier malfunction, that is, the movement of the sheet through the work station is either partially or substantially hindered. In either event, the sheet is exposed to image-fixing heat energy for too long a time and is damaged, thereby making the reproduced image unsatisfactory.